I too was pool stored. But not too much. Not sure if I had metal or organic stains, but the pool I bought with the house is large in ground, 31,000 gallons and older. On top, it had not been opened for 3 years when I got here.
Pattern is only on the upper out of water sides, rest has gone virtually white. Old I guess. Probably needs replacing, but I have been taking care of it myself. Never owned a pool before. All seems well except this year I decided to tackle the staining. Up sides to water line at 90% of pool (tea color as someone mentioned). 80% of bottom too. How come worms and leaves leave white clean space? get to that later).
Read about Ascorbic powder on this site. Went about trying it. Yes on the whole pool. Sides first. Ordered 5 pounds on line. Tried a bit and it worked like a majic eraser. Except it dissolved before I could do much of an area.
So, I bought a camille car washer wand screwed it to an old broom stick and tried to spoon the powder tween the outer sock and the inner sponge. Worked better, still too much dissolve. Was able to do two square feet per load. Scrubbing doesnt help, longer it sat on the stain the better. So, I took a piece of the gardening "weed block cloth" and put in inside the outer sock to keep the rate of dissolve down. It helped alot. Got to 4 square feet per 3 tablespoons of powder.
Took 5 pounds to do half of sides so I ordered another 10 (cheaper per pound) to do rest and bottom.
Did a phenomenal job. People couldn't believe it. Admittedly, some spots have returned but nothing like what I had. It really worked. Wish I could figure out how to make the clean up permanent. Did a great job on the rust and scale build up a the scimmer frame too.
good luck. If anyone has an idea on the recurring of stains in some area please respond. Oh, I did have issures with clorine ppm going way down even with auto feeder, but PH remained good and I recharged DE filter twice tween cleanings over two weeks, shocking as normal and all readings returned to good.
